Gaseous fuel powered engines are common in locomotive applications. For example, the engines of a locomotive can be powered by natural gas alone or by a mixture of natural gas and diesel fuel. Due to environmental and economic drivers, a primary source of fuel for engines of locomotives is becoming liquid natural gas (LNG). LNG has a lower volumetric energy density than diesel fuel, thus leading to the storage of the LNG in a separate fuel tender. In order to maintain the LNG in a liquid state at atmospheric pressures, the LNG must be stored in a cryogenic, insulated tank capable of maintaining the temperature of the LNG below −165 degrees Centigrade. While a majority of the LNG remains liquid without refrigeration for a period of time that may be as long as several weeks, a portion of the LNG within the tank may boil off into methane gas as heat is absorbed from the environment. This methane gas accumulates as a vapor above the LNG in the storage tank. The accumulated gas cannot be used as part of the LNG fuel source and is typically vented to the surrounding environment, thus reducing the efficiency of the system.
One attempt to improve the efficiency of a fuel powered engine is disclosed in U.S. Pat. No. 4,924,822 (the '822 patent) issued to Asai et al. on May 15, 1990. The '822 patent describes a gas feed system for a diesel engine. A boil-off gas evaporated from a liquefied gas is fed to the diesel engine either alone or in combination with the liquefied gas. The boil-off gas is pressurized in one or more streams before being fed to the diesel engine through one or more gas feed pipes.
Although the system of the '822 patent may enable the boil-off gas to be partially recovered for use in the diesel engine, the system may not enable full recovery and use of the boil-off gas. For example, when the diesel engine is idling, operating on low power, or not operational, the boil-off gas may need to be vented to the surrounding environment since the engine may not be configured to receive a low pressure flow of gas.
The presently disclosed fuel system is directed to addressing one or more of the problems set forth above.